You don't need to do that. All that did was create a folder named thelab.dierrelabs.info. So now when your parked domain goes into effect you will have a folder like this:
http://thelab.dierrelabs.info/thelab.dierrelabs.info
Also you need to point your domain to both of our nameservers, not just ns1. You should see two seperate forms at your domain name provider to add both, like this:
ns1.heliohost.org
ns2.heliohost.org
When I checked your domain name all I saw was the first nameserver.
Yeah, I know but it does not allow that. My dierrelabs.info domain is pointing to the dns of my main host (which hosts my main site) so I wanted to try to add a subdomain as an NS node but after I've inserted the first thelab -> ns1... then I can't add a second thelab -> ns2... so I think I can't do that.